Brush holder



Aug, 13, 1935. F, H. PRITCHARD 2,011,374

' BRUSH HOLDER Filed Oct. 12, 1932 2 Sheets-Sheet l 7 Inventow:

Franklin IE-LPvitchamd,

His Aot oPne L Aug. 13, 1935. PRITCHARD 2,011,374

BRUSH HOLDER Filed Oct. 12, 1932 2 Sheets-Sheet 2 Invent OYI Fhanklin H.PYi O chahd,

His Attobne Patented Aug. 13, 1935 UNITED STATES PATENT orrics BRUSH HOLDER New York Application October 12, 1932, Serial No. 637,449 '2 Claims. (01. 171?324.)'

My invention relates to brush holders for dynamo-electric machines.

In the designing of modern alternating current railway motors it has been found necessary to increase the number of poles for a given diameter of armature and in some instances the number of poles for a given motor has been doubled. The space available for brush holders in the new de sign is not sufiicient to accommodate the required number of brush holders of the ordinary type used in railway motor construction. For this reason it is necessary to provide a type of brush holder'having the necessary brush feeding and pressure characteristics and occupying a small space.

The object of my invention is to provide a simple and compact brush holder of improved construction for dynamo-electric machines, in which substantially constant brush pressure is obtained.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawings in which Fig. 1 is a side elevation partly in section oi a pair of brush holders embodying my invention mounted on a brush yoke; Fig. 2 is a perspective view of one of the brush fingers; Fig. 3 is a perspective view from the brush guide side of the right hand brush holder of Fig. 1; and Fig. 4 is a perspective view of the other side of Fig. 3 with the brush guide and pressure fingers removed.

Referring now to Fig. l, I have shown a pair of brush holders l0 each being of the same con.- struction except that they are made for right and left mounting, respectively. "The brush holders ID are secured to insulating studs H by capscrews I2, the studs being secured to the brush yoke i3 by threaded connections M. Each of the brush holders comprises a main body and an arm or bracket l6 formed integrally therewith, and a brush guide block ll. positioned on the main body 15 by a rabbeted joint and secured thereto by capscrews 18. The construction of the brush holders can best be seen in Figs. 3 and 4, where it will be noted that each of the holders has been shown as constructed to accommodate five brushes. As shown in Fig. 1, the brush holders are provided with pressure fingers l9 actuated by compression springs for urging carbon brushes 2| through the guides Na in the block I! into contact with a current collecting device. The brush guides are provided with openings or slots 22 in the center thereof, so that the brush pressure fingers I9 may follow the brush down through the guide as the brush becomes worn. Compression springs 20 are located in recesses 23 in the main body of the brush support. It will be noted that this makes possible a 'very compact construction.

The construction and arrangement of the brush pressure fingers (9 can best be seen by referring to Figs. 1 and 2. These brush pressure fingers are made of a light construction in order that they shall have little inertia and consequently may easily follow the brush in its vibrating movement-caused by irregularities in the surface of the commutator. Each brush pressure finger [9 comprises a U-shaped bracket 24 to which are secured a fiat spring 25 and a conductor strip 26 spaced apart at their mid-portions, as shown, and held together at their outer ends by a contact piece 21 engaging the top of the carbon brushes 2 I. The conducting strip 26 is bent around the fiat spring and the top of the bracket and extends over the upturned lug 24a on the bracket. A strip of metal 28 extends about the U-shaped bracket, the conducting strip 26 and the several parts are held together by the rivets 2%. The current leads 30 for the brushes are secured to the upturned lug 24a by a screw 3|. The U-shaped bracket 24 is provided with bosses 25b and a bearing 32 which is insulated from the bracket and the bosses by an insulated bushing 33. This insulated bushing is provided in order to prevent the passage of current between thesupporting arm and the bracket 24. which would produce pitting and undesirable deterioration of the bearings. Several brush pressure fingers l9 are secured to the main body of the brush holders 10 by a pin 34 which passes through the lugs 35 formed on the main body l5 of the brush holders, insulating washers 33' being provided to insulate the ends of the bosses 24b from the lugs 35. In order to transmit the thrust of the compression spring 23 to the brush pressure finger IS the U-shaped bracket 24 is provided with a pin 36 across the ends of the bracket. This pin engages an insulating thrust transmitting block 31 which is seated in the end of the spring 253. It will be apparent that the thrust of the spring 20 against the bracket 24 will urge the brush pressure finger 19 against the brush 2| and maintain contact between the brush and the commutator or other current collecting device with which it is employed. In this brush holder construction the pressure finger is arranged in close proximity to the brush guide and since the compression spring is located between the brush guide and the pressure finger pivot, the space is saved which is oocupied in the ordinary type of holder by spiral or helical springs extending about the finger pivot. This results in a very compact construction making possible the use of shorter supporting arms and closer grouping of the sets of brushes.

Referring to the sectional view of the brush pressure finger [9 shown on the left hand brush holder of Fig. 1, it will be noted that as the bracket 24 is rotated about the pin 34 by the compression spring 20, the effective lever arm of the spring about the pin 34 will be increased, or, in other words, the distance between the pin 34 and the line of application of the force of the spring 20 will be increased. According to my invention the brush fingers and the spring 20 are so related that this increase will be effective throughbrush pressure fingers 19 will follow themandwill maintain substantially constant pressure between the brush and the surface of the moving current collecting surface. At the same time, the low inertia construction of the brush pressure fingers enables them to easily follow any variations in movement due to the irregularities of the commutator when it is-running at high speed which is essential to the maintenance of even distribution of current between the brushes and the avoidance of destructive arcing.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A brush holder for dynamo-electric machines including a brush guide, a pressure finger for urging a brush through said guide, means for pivotally supporting said finger at one side of said guide, means including a compression spring arranged between said guide and said pivotal support for actuating said pressure finger, and means for preventing passage of current from said pressure finger through said pivotal support and through said compression spring.

2. A brush holder for dynamo-electric machines including a brushguide, a low inertia pressure finger for urging a brush through said guide, meansfor pivotally supporting said finger at one side of said guide, a compression spring arranged between said guide-and said pivotal support for actuating said pressure finger, and means for preventing passage of current from saidpressure finger through said pivotal support and through said compression spring.

3. A brush holder for dynamo-electric machines including a brush guide, a pressure finger for urging a brush through said guide, means including a bracket secured to said pressure finger for pivotally supporting said finger at one side of said guide, means including a compression spring arranged between said guide and said bracket for actuating said pressure finger, and means for preventing passage of current from said pressure finger through said pivotal support and through said compression spring.

4. A brush holder for dynamo-electric machines including a'brush guide, a pressure finger for urging a brush through said guide, means including a sleeve of insulating material for pivotally supporting said finger at one side of said guide, a thrust block of insulating material pivoted on said pivotally supporting means, and a compression spring engaging said thrust blockand arranged between said block and said guide for actuating said pressure finger. v I

5. A brush holder for dynamo-electric machines including a brush guide, means including a pressure finger pivotally supported atone side of said guide for urging a brush through said guide, means for preventing passage of current from said pressure finger through the pivotal support therefor, means including a-compression spring arranged between said guide and said pressure finger for actuating said pressure finger, and means including an insulating thrust block pivoted on said pressure finger and engaging said compression spring for increasing the effective lever arm of said compression spring aboutthe pivotal support of said pressure finger as said compression spring is extended. 7 6. A brush pressure finger. comprising a,'-U-

shaped bracket, a flat spring, a strip of metal of high electrical conductivity folded about said bracket and one end of said spring, means for securing said bracket said spring and said strip together at said one end, a brush contact piece.

secured to said spring and said strip near the other end of said spring, and means for connect-. 

